An improved mounting assembly is provided that is configured to be releasably attached to a standard dovetail rail profile, wherein the initial clamping tension of a clamping assembly is adjustable. The mounting assembly includes a main body having a lower portion that is configured to engage a standard dovetail and an upper portion accessory receiving formation. The lower portion of the mounting assembly has a first engagement member extending downwardly along one side thereof for engaging one side of the dovetail rail and a clamping assembly to engage the opposing side of the dovetail rail. At least one spring and a retention nut are provided as part of the clamping assembly such that retention nut controls the preset spring tension thereby controlling the clamping force applied by the clamping assembly. A lock lever connected to the actuator arm selectively locks the position of the retention nut on the threaded shaft.